Headlamp assemblies are used in all types of vehicles including, automobiles, airplanes, motorcycles, off-road equipment, and the like. Traditionally, in the automotive business, a new headlamp assembly would be designed and manufactured for each car that was to be manufactured. This required automotive design engineers to first consider the envelope the entire headlamp assembly was to encompass. Once the envelope was established, an entire headlamp assembly could be designed to specifically fit that particular envelope. Each assembly would contain a variety of components including an outer cover lens, a reflector, a light source and a body or frame to support the light source and reflector. Because designing a new headlamp assembly for each car model is costly, it would be preferred to standardize as many of these components as possible and to use the standardized parts in as many different makes of automobiles as possible. Thus, there is a need for a reflector and light source unit that can be utilized with various headlamp support frames in numerous automobiles. The headlamp reflector of the headlamp assembly must be carefully designed so that the resulting illumination beam has the required intensity distribution pattern.
Conventional headlamp beam patterns require a sharp cutoff line that is parallel to the horizon and a beam width of plus or minus thirty degrees. This defines the maximum vertical extent of the beam as well as the minimum horizontal spread of the beam. This combination of horizon line cutoff and controlled horizontal spread is typical of all foreign and domestic (low-beam) headlamp beam patterns.
When designing a headlamp assembly, it is preferred to have a headlamp beam pattern that is as smooth as possible. It is also preferred to have a headlamp reflector that generates a beam pattern that does not create any localized hot spots on the clear cover lens. It is further preferred to have a headlamp assembly comprised of a reflector constructed of a minimal number of segments or facets, each contributing some portion of the beam pattern. The resulting reflector, by virtue of smaller size and reduced feature count, will be less costly to manufacture and can be used in several different headlamp assemblies. The smaller size and reduced feature count are made possible by a unique geometric definition of the reflector surface.
According to one aspect of the invention, an automotive headlamp reflector unit is comprised of a one-piece light reflector with a light source mounted generally in the middle of the reflector. The reflector is formed of separate curved segments that are arranged to form a composite reflective surface. Each segment is shaped to provide an optimum reflected light pattern. All of the reflected light patterns together form a composite light pattern to satisfy legal, safety and aesthetic requirements.
The relatively smaller size of the reflector unit allows its installation within the confines of a variety of different sizes and shapes of headlamp support frames. A decorative bezel would typically fill the space between the functional reflector and the support frame. While the reflector could be common across several vehicle types, the optically non-functional bezel would be a custom interface between the functional reflector and its support frame.
The cost of designing and building a custom bezel is substantially less than the cost of designing and building a custom headlamp, because there are no optical requirements other than to not block the light from the headlamp.
According to another aspect of the invention, a smooth beam pattern is obtained by allowing the reflected images of the light source to he smeared or unfocused in the horizontal direction while a sharp horizontal line cutoff is obtained because the light rays are kept parallel to the ground. Each reflector facet transforms a nominally spherical wavefront from a point light source, i.e., bulb, into a cylindrical wavefront with a vertical axis. A portion of a (vertical) cylindrical wavefront is ideal for headlamp design because it is characterized by zero vertical light spreading and arbitrary horizontal light spreading.
The surface of the reflector is designed by taking into consideration the coordinates of an ideal point light source and the coordinates of the axis of a cylindrical wavefront. The axis of the cylindrical wavefront is oriented vertically so that the vertical spread of the reflected beam is zero. This minimizes the ability of the reflected beam of light to diverge or converge vertically. The horizontal spread, however, is controlled by the width and the location of the reflector relative to the axis of the cylindrical wavefront. When the axis of the cylindrical wavefront is behind the reflector, the lamp output is strictly diverging, and no focal hot spots will form on the clear cover lens. This is particularly important for smaller lamps, to avoid thermal damage to the cover lens.
The physical configuration of the reflector is itself defined mathematically by considering the optical path difference between a ray of light from the light source and a ray of light from the cylindrical axis.
According to yet another aspect of the invention, a headlamp reflector assembly is comprised of a light source that is located approximately in the middle of and surrounded by a generally concave dish-like reflective surface. The light source is operable to emit light waves that diverge onto the reflector yet reflect off substantially parallel to the ground.
The reflector is offset from the light source and has preferably eight to twelve reflective segments. The segments together define the entire reflective surface which reflects a beam of light composed of a collection of nominally cylindrical wavefronts through a lens. Because of the design of the resulting beam of light, hot spots on the surface of the lens are minimized.
For the following specification taken in conjunction with the accompanying drawings and appended claims, other objects, features, and advantages of the present invention will become apparent to those skilled in the art.